The present invention relates to the field of centrifuges. More particularly, the invention comprises a device for removing hard sludge automatically from the interior of a centrifuge basket.
In a basket centrifuge, a liquid containing solid material is directed into a rapidly rotating basket. As the basket spins, the solid particles in the liquid migrate to the basket wall, due to centrifugal force. As more and more liquid/solid mixture is added to the basket, the clarified liquid overflows the sides of the basket, while the solid material remains trapped along the basket wall. The clean liquid is then recovered by suitable collecting means outside the basket.
After prolonged use of the centrifuge, there is a substantial accumulation of solid material along the basket wall. This material, referred to generally as "sludge", reduces the efficiency of the centrifuge by occupying space that would otherwise be filled with liquid. The sludge must therefore be periodically removed in order to enable the centrifuge to process additional liquid at the normal rate.
Sludge is generally classified in two groups. There is the socalled "soft" or gelatinous sludge, such as that which results from the separation of impurities from several industrial processes, such as electroplating, degreasing, or paint spraying. The other kind of sludge is "hard" sludge, which results from metal fines, glass fines, sugar crystals, and the like. This invention is directed to the special problems associated with hard sludge.
Soft sludge may be conveniently removed from a centrifuge basket by introducing a discharge tube into the centrifuge while the basket is spinning. The relative motion of the basket and the tube causes the soft sludge to be extruded through the tube, and discharged into an appropriate collection container. The tube need only be moved radially, i.e. towards and away from the rim of the basket. The tube need not be moved vertically within the basket, since the soft sludge will migrate in a vertical direction towards the tube.
Hard sludge is not as easily removed from a centrifuge. Not only does hard sludge tend to clog the discharge tube, but it becomes firmly packed along the basket wall, and does not migrate vertically to the location of the tube. The simple expedient of using a single discharge tube, which is satisfactory for soft sludge, will not work satisfactorily for hard sludge.
The problem of removing solid particles from centrifuge components has been addressed in various ways in the prior art. For example, U.S. Pat. No. 3,682,310 shows a centrifuge having a filter disposed therein. A stream of air is periodically directed against the filter to loosen particles which have accumulated on the filter element. U.S. Pat. No. 4,000,074 shows a centrifuge wherein dried particles of explosive material fall out of the centrifuge by gravity. U.S. Pat. No. 2,206,401 uses a spray means directed into the centrifuge basket, apparently to inject a washing agent into the apparatus. U.S. Pat. No. 614,764 shows a centrifuge for separating sugar syrup from sugar crystals, wherein the crystals are removed from the bottom of the apparatus. U.S. Pat. No. 3,311,240 shows another sugar centrifuge, including a spray means for washing or coating the solid particles.
Nothing in the known prior art teaches a satisfactory automatic method for removal of hard sludge. The only known prior art technique for automatically scraping hard sludge from the basket wall requires actuated blades to "plow" the material loose. This technique is a slow-speed process, and requires high power. In addition to the need for specialized drive components, this prior art technique requires parts which wear rapidly, due to the abrasive character of the sludges.
The only alternative to the above-described technique has been manual cleaning. It has been necessary to stop the centrifuge, remove the basket, and replace it with a spare basket, while the original basket is cleaned by hand. This procedure is cumbersome and inefficient. Not only is it difficult to remove the sludge manually, but the method requires that the system be stopped every time a cleaning is necessary.
The present invention provides an apparatus which overcomes the above-described difficulties in removing hard sludge from a centrifuge. The invention requires only minimal contact with the abrasive sludge, in the re-slurrying process. The invention also comprises a method of removing such sludge. By use of the present invention, sludge may be removed from a centrifuge basket without manual cleaning, and without stopping the entire system. The invention may be used to remove many different kinds of hard sludge, having different degrees of hardness.